Review on the two-stage vapor injection heat pump with a flash tank

Abstract

Refrigerant vapor injection technology is a reliable method to reduce the discharge temperature and improve the heating performance of air source heat pumps at low ambient temperatures. Compressor technology, injection configuration, and the state of injected refrigerant significantly affect system performance, complexity and initial investment. The flash tank injection system demonstrates a better system performance than the heat exchanger system, but the lack of an appropriate control strategy is a factor that hinders the widespread use of the flash tank system. To reveal the challenges of the system, this paper reviews the parameters affecting the system performance and the control strategies on two-stage vapor injected heat pumps with a flash tank. ESC, a model-independent real-time control strategy, is presented as a promising solution for optimal control of the FTC cycle. The performance of the system is influenced by factors such as de-superheating, subcooling, injection mass flow rate, injection pressure and variable speed. Injection pressure is the main factor. There exists an optimal injection pressure to maximize the COP of the system.